Mobile devices, such as but not limited to personal data appliances, cellular phones, radios, pagers, lap top computers, and the like are required to operate for relatively long periods before being recharged. These mobile devices usually include one or more processors as well as multiple memory modules and other peripheral devices.
The power consumption of a transistor-based device is highly influenced by leakage currents that flow through the transistor. The leakage current is responsive to various parameters including the threshold voltage (Vt) of the transistor, the temperature of the transistor and the like. Transistors that have higher Vt are relatively slower but have lower leakage currents while transistors that have lower Vt are relatively faster but have higher leakage current.
In order to reduce the power consumption of mobile devices various power consumption control techniques were suggested. A first technique includes reducing the clock frequency of the mobile device. A second technique is known as dynamic voltage scaling (DVS) or alternatively is known as dynamic voltage and frequency scaling (DVFS) and includes altering the voltage that is supplied to a processor as well as altering the frequency of a clock signal that is provided to the processor in response to the computational load demands (also referred to as throughput) of the processor. Higher voltage levels are associated with higher operating frequencies and higher computational load but are also associated with higher energy consumption.
A third technique uses domino circuits that include both high threshold voltage transistors and low threshold voltage transistors. U.S. patent application number 2004/0008056 of Kursun et al., which is incorporated herein by reference, discloses a domino circuit that is configured such as to reduce power consumption, for example by limiting the energy consumed during power switching.
Yet another technique is based upon creating a stack effect that involves shutting down multiple transistors of the same type that are serially connected to each other. U.S. Pat. No. 6,169,419 of De et al., which is incorporated herein by reference, discloses a method and apparatus for reducing standby leakage current using a transistor stack effect. De describes a logic that has both a pull up path and a pull down path.
There is a growing need to find effective devices and methods for reducing power consumption of integrated circuits.